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<title>nsss: the nsss library interface</title>
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<p>
<a href="../">nsss</a><br />
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">skarnet.org</a>
</p>
<h1> The <tt>nsss</tt> library interface </h1>
<h2> General information </h2>
<p>
<tt>libnsss</tt> is the generic name for the nsss client library.
This library is made of several parts:
</p>
<ul>
<li> <a href="nsss-unix.html">nsss-unix</a>: this is a set of
functions to access the <tt>/etc/passwd</tt>, <tt>/etc/group</tt>
and <tt>/etc/shadow</tt> files. </li>
<li> <a href="nsss-switch.html">nsss-switch</a>: this is a set of
functions to connect to a <em>nsssd-service</em> and interact with
various server-side daemons such as
<a href="../nsssd-unix.html">nsssd-unix</a> or
<a href="../nsssd-nslcd.html">nsssd-nslcd</a>. </li>
<li> nsss-all: this is a set of
functions that try connecting to a nsssd service first, and fall
back to the <a href="nsss-unix.html">nsss-unix</a> implementation
if the connection fails (no nsssd service is running). </li>
</ul>
<p>
Both <a href="nsss-unix.html">nsss-unix</a> and
<a href="nsss-switch.html">nsss-switch</a> are made of two parts:
</p>
<ul>
<li> An internal, clean API, that applications can use directly
if they include the <tt>nsss/nsss.h</tt> header, or the relevant
<tt>nsss/nsss-unix.h</tt> or <tt>nsss/nsss-switch.h</tt> header. </li>
<li> As a series of thin wrappers around the internal API, an
implementation of the standard following functions:
<ul>
<li> endpwent() </li>
<li> setpwent() </li>
<li> getpwent() </li>
<li> getpwent_r() </li>
<li> getpwuid() </li>
<li> getpwuid_r() </li>
<li> getpwnam() </li>
<li> getpwnam_r() </li>
<li> endgrent() </li>
<li> setgrent() </li>
<li> getgrent() </li>
<li> getgrent_r() </li>
<li> getgrgid() </li>
<li> getgrgid_r() </li>
<li> getgrnam() </li>
<li> getgrnam_r() </li>
<li> endspent() </li>
<li> setspent() </li>
<li> getspent() </li>
<li> getspent_r() </li>
<li> getspnam() </li>
<li> getspnam_r() </li>
</ul> </li>
The functions are prefixed with <tt>nsss_unix_</tt> or
<tt>nsss_switch_</tt>. For instance, <tt>nsss_unix_getpwnam()</tt>
is the implementation of <tt>getpwnam()</tt> that uses the
<tt>/etc/passwd</tt> backend. </li>
</ul>
<p>
nsss-all does not have an internal API. It only contains the
implementation of the above standard functions, as
<tt>nsss_all_getpwnam()</tt> and similar.
</p>
<h2> Compiling </h2>
<p>
Application programs can use the internal API directly, or
the prefixed <tt>nsss_</tt> functions directly. Most programs,
however, will simply use the standard
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/pwd.h.html">pwd.h</a>,
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/grp.h.html">grp.h</a> or
<a href="http://man7.org/linux/man-pages/man3/getspnam.3.html">shadow.h</a>
interfaces. nsss provides a version of these standard headers: if an
application is built with these headers, then <tt>getpwnam()</tt>
will automatically be aliased to <tt>nsss_all_getpwnam()</tt>, and
the other functions will be aliased similarly.
</p>
<p>
If the NSSS_DISABLE_SWITCH macro is defined before inclusion of the
nsss headers, then <tt>getpwnam()</tt> will be aliased to
<tt>nsss_unix_getpwnam()</tt> instead, and the other functions will
follow the same pattern. If, instead, the NSSS_DISABLE_UNIX macro
is defined before inclusion of the nsss headers, then <tt>getpwnam()</tt>
will be aliased to <tt>nsss_switch_getpwnam()</tt>, and the other
functions will follow the same pattern.
</p>
<p>
So, the proper steps to compile an application with libnsss are:
</p>
<ul>
<li> Make sure the nsss headers, as well as the skalibs headers,
are visible in your header search path. </li>
<li> Use <tt>#include <nsss/nsss.h></tt> </li>
<li> To use the standard <tt>pwd.h</tt> interface, you can
just <tt>#include <pwd.h></tt>, which will work as long
as the <tt>nsss/pwd.h</tt> header is accessible in your header
search path. </li>
<li> Same thing for <tt>grp.h</tt> and <tt>shadow.h</tt>. </li>
<li> If don't want to use the nsss-all implementation of
"try nsss-switch and fall back to nsss-unix if it fails", then
compile with -DNSSS_DISABLE_SWITCH or -DNSSS_DISABLE_UNIX as
desired. </li>
</ul>
<h2> Linking </h2>
<ul>
<li> Make sure the nsss library, as well as the skalibs library,
are visible in your library search path. </li>
<li> Link against <tt>-lnsss</tt>, <tt>-lskarnet</tt>, <tt>-lpthread</tt>,
<tt>`cat $SYSDEPS/socket.lib`</tt> and
<tt>`cat $SYSDEPS/sysclock.lib`</tt>, $SYSDEPS being your skalibs
sysdeps directory. </li>
</ul>
<h2> Programming </h2>
<ul>
<li> nsss-all, nsss-switch and nsss-unix implement the
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/getpwnam.html">POSIX
layer</a> of user database access, plus a few
<a href="http://man7.org/linux/man-pages/man3/getpwent_r.3.html">GNU extensions</a>. </li>
<li> The <a href="nsss-unix.html">nsss/nsss-unix.h</a> header
can be used to access the internal nsss-unix API. </li>
<li> The <a href="nsss-switch.html">nsss/nsss-switch.h</a> header
can be used to access the internal nsss-switch API. </li>
</ul>
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